The number of echoes combined into a single image or image set in multiple echo imaging sequences or echo-train techniques such as rapid acquisition with relaxation enhancement (RARE), fast-spin echo (FSE), and turbo spin-echo (TSE). In RARE imaging, the ETL typically equals the acceleration factor.
As for tooth pain, it is caused by a reaction of the nerves inside a tooth's pulp chamber with the severity dependent upon the type and degree of the stimulus. What follows are some examples of symptoms you may be feeling and their possible causes.
Pain is associated with swelling of the gums or face, or you have discharge around a tooth; fever is an important sign of infection in dental disease. Simple dental decay (caries) does not cause fever. These signs may signify an infection surrounding the tooth, the gum, or the jaw bone (mandible).